I recommend the Topeak MTX system, you can get the rack and bag with foldout panniers for less than $100: http://www.modernbike.com/search.asp...=17&submit.y=8

I went with the DXP. It isn't that much larger or heavier, even though the capacity is greater.

If you don't have eyelets down on the chain/seat stay area, they also have seat post mounted racks compatible with the MTX bags: http://www.topeak.com/products/Racks Then lastly, if you don't have eyelets on the seat stays near the seat, then get some p-clamps from your LBS or hardware store.